1. Field of the Invention
The present invention relates to a process of producing lithium nickel oxide and also to a nonaqueous secondary battery using said lithium nickel oxide as an active material for positive electrode.
2. Related Art
In the Japanese Unexamined Patent Publication No. Hei 02(1990)-040,861, lithium nickel oxide is manufactured as follows. Solid lithium hydroxide and solid nickel oxide are mixed, the mixture is calcined in an atmospheric condition at 600.degree. C. and the calcined product is pulverized and again calcined at 600.degree. C. to 800.degree. C. whereupon lithium nickel oxide is manufactured.
In the Japanese Unexamined Patent Publication No. Hei 05(1993)-251,079, solid lithium nitrate is mixed with at least one of solid nickel hydroxide and nickel oxyhydroxide and calcined at 500.degree. C. to 1000.degree. C. whereupon lithium nickel oxide is manufactured.
In the Japanese Unexamined Patent Publication No. Hei 06(1994)-044,970, a lithium nickel composite oxide is manufactured as follows. To a saturated aqueous solution containing at least one nickel salt selected from nickel halide, nickel sulfate, nickel phosphate, nickel acetate and nickel oxalate is added a saturated aqueous solution containing at least one lithium salt selected from lithium hydroxide, lithium carbonate and lithium hydrogencarbonate where said lithium salt is equimolar to the above nickel salt. The mixed solution is then evaporated to dryness with stirring and mixing in air or in vacuo and the resulting caky solid mixture is calcined at 600.degree. C. to 800.degree. C. whereupon a lithium nickel composite oxide is manufactured.
In the Japanese Unexamined Patent Publication No. Hei 06(1994)-044,971, a lithium nickel composite oxide is manufactured as follows. To at least one powdery nickel compound which is slightly soluble or insoluble in water selected from nickel oxide, nickel oxyhydroxide, nickel hydroxide and nickel carbonate is added a saturated aqueous solution of at least one lithium salt selected from lithium halide, lithium nitrate, lithium sulfate, lithium phosphate, lithium borate, lithium acetate and lithium oxalate followed by well kneading. This mixture is evaporated to dryness with stirring in air or in vacuo and the resulting caky solid mixture is calcined at 600.degree. C. to 800.degree. C. whereupon a lithium nickel composite oxide is manufactured.
In the Japanese Unexamined Patent Publication No. Hei 06(1994)-096,769, lithium nickel oxide is manufactured as follows. A lithium source and a nickel source are mixed so as to make the molar ratio of lithium in the lithium source to nickel in the nickel source 1:1. At that time, a small amount of water is added as a dispersing medium to the mixture. The resulting mixture is dried and calcined at 650.degree. C. to 800.degree. C. whereupon lithium nickel oxide is manufactured.
However, in the manufacturing processes of lithium nickel oxide mentioned in the Japanese Unexamined Patent Publications Nos. Hei 02(1990)-040,861 and Hei 05(1993)-251,079, a lithium compound and a nickel compound in a solid state are mixed and, therefore, it is difficult to mix them homogeneously.
In the manufacturing process of a lithium nickel composite oxide mentioned in the Japanese Unexamined Patent Publication No. Hei 06(1994)-044,970, lithium compound and nickel compound are mixed in a state of aqueous solution. However, in the steps of drying and solidifying the aqueous solution, deposition of the solutes does not take place simultaneously because solubilities of the solutes are different. Accordingly, in the resulting caky solid mixture, the lithium and nickel compounds are hardly mixed homogeneously.
In the manufacturing processes of lithium nickel oxide mentioned in the Japanese Unexamined Patent Publications Nos. Hei 06(1994)-044,971 and Hei 06(1994)-096,769, a mixing is conducted using water as a dispersing medium. However, in drying the mixture, the substances dissolved in the dispersing medium are not deposited uniformly. Therefore, the lithium compound and the nickel compound are not well mixed in the resulting mixture.
In a nonaqueous secondary battery where lithium nickel oxide obtained by calcining a mixture which is not sufficiently mixed is used as a positive electrode active material, a discharge capacity (hereinafter, just referred to as "capacity") significantly decreases upon repeated charging/discharging operations and the electrodes are quickly deteriorated.